1. Field of the Invention
This invention relates to a drilling tool, in particular a drill which has chip flutes for the removal of the chips, the drill cutting parts of which are formed by replaceable cutting elements. In the design of drills, one general problem is that the material of which the drill is made must on one hand be sufficiently hard and resistant to wear and abrasion, so that in the cutting area of the drill, the desired cutting action can be guaranteed over a long period. On the other hand, however, the drill must be sufficiently tough to withstand the torsional vibrations to which it is subjected during drilling. On drills of the prior art, this problem is solved by fabricating the drill using a material which is capable of withstanding the above-mentioned vibrations and has sufficient toughness, but which is therefore somewhat less resistant to wear, and the cutting parts are formed by replaceable cutting elements. Such replaceable cutting elements are also realized in the form of replaceable inserts. For the sake of simplicity, therefore, the term "replaceable inserts" will be used in the remainder of this description. In drills, the chip which has been removed from the workpiece, after the chip has been deflected by the face of the replaceable insert in the chip removal direction, is guided at a more or less acute angle toward the chip flute wall, where it is deformed into a spiral or a helical chip. The purpose of the deformation is to generate a chip spiral, the diameter of which is less than the depth of the chip space, i.e. the radial distance between the drill web and the wall of the drill-hole formed by the drill. A chip spiral shaped in this manner specifically comes into contact with the wall of the drill-hole only to an insignificant extent; it is transported away primarily with friction against the wall of the chip flute. The surface of the wall of the drill-hole is thereby protected.
2. Background Information
On account of the material of which the drill is made, which material has lower resistance to wear, however, the chip shaping area described above which is active in the deformation of the chip is subject to increased wear and abrasion. While the indexable inserts are designed to have a relatively long useful life, the above-mentioned wear causes uncontrolled changes in the chip shaping area, which can in particular be eroded in a concave fashion. The original chip shaping characteristics of the chip shaping area are thereby lost. One of several consequences of this situation is that the chip is deflected against the wall of the drill-hole, and as the chip is being removed, it rubs against the wall, as a result of which the surface quality of the wall of the drill-hole deteriorates. The wear of the chip shaping area can also result in the rupture of the chip. The chip fragments can become wedged in the chip space which is formed by the chip flute and the wall of the drill-hole, and can also have an adverse effect on the surface quality of the wall of the drill-hole. Chip fragments can even become jammed between the drill and the wall of the drill-hole, which results in a severe heating and finally a "welding" of the drill.